Electronic structure and optical properties of complex hydrides LiBH4 and NaAlH4 compounds

Summary The properties of the complex hydrides LiBH 4 and NaAlH 4 such as structural, electronic, and optical properties were calculated using the augmented plane wave plus local orbitals (APW + lo) method. The three phases α , β , and γ of LiBH 4 and NaAlH 4 hydrides are studied, the β ‐phase is transformed at the high‐pressure to γ phase for the compound LiBH 4 with the generalized gradient approximation (GGA) with a 16% volume decrease. However, NaAlH 4 compound did not show any phase transition. The interaction between the boron (aluminum) atoms and the hydrogen atoms in the [AlH 4 ] − ( [BH 4 ] − ) complexes is strongly covalent, and between the complexes [AlH 4 ] − and the lithium Li + cations for the LiBH 4 compound and between the complexes [AlH 4 ] − and the sodium Na + cations for the NaAlH 4 compound, the bond is ionic. For the most stable phases of the two complex hydrides, different optical parameters have been calculated as a function of the photon energy. The plasma frequency ω p is calculated from the mean peak of the energy loss function. Therefore, by way of example, the plasma energy ħω p of its peak position is 13.23 (12.93) eV for α‐ NaAlH 4 ( α‐ LiBH 4 ).